Lettuce big-vein virus (LBVV) is a virus belonging to Varicosavirus, is composed of two RNAs (7.0 kb and 6.5 kb RNA), and retains a coat protein of 48 kDa. LBVV is a soil-borne virus that is spread in the soil by Olpidum brassicae, and occurs in the United States, Australia, New Zealand, Japan and Europe. Since this virus infects lettuce and remarkably lowers its quality and yield, it is a serious problem in lettuce production.
Unfortunately, there has not yet been reported the existence of a gene that makes lettuce resistant to this virus. Although several cultivars such as Entree, Sea Green and Pacific are commercially available as LBVV-resistant cultivars, their resistance is low. Thus, there has not yet been found a radical solution to disease damage caused by LBVV.
Elucidation of the virus genetic information is an important step in preventing disease damage caused by the virus. However, isolation and purification of LBVV are extremely difficult for reasons such as the instability of the viral particles, tendency for viral particles to readily aggregate with each other, and extremely low concentration of the virus in plants. Although, so far, two successful examples of purification of the virus have been reported (S. Kuwata et al., (1983), Annals of the Phytopathological Society of Japan, 49, 246-251; and, H. J. Vetten et al. (1987), Journal of Phytopathology, 120, 53-59), the reproducibility is low and the purified amounts are extremely low. Consequently, as to LBVV, no genetic information has been elucidated at all.